Role of Central Atom on the Pressure Response of 2D Perovskites Containing a Long Alkyl Chain (Decylammonium, DA): DA2PbI4 and DA2GeI4

The application of an external pressure on Metal Halide Perovskite (MHPs) has become a fascinating way of tuning their optical properties, achieving also novel features. Here, the pressure response of 2D MHPs including a long alkyl chain made of ten carbon atoms, namely decylammonium (DA), has been investigated as a function of the central atom in DA2PbI4 and DA2GeI4. The two systems share a common trend in the phase stability, displaying a transition from an orthorhombic to a monoclinic phase around 2 GPa, followed by a phase separation in two monoclinic phases characterized by different c-axis. The optical properties show rather different behavior due to the presence of Pb or Ge. DA2PbI4 shows a progressive red shift of the band gap from 2.28 eV at ambient conditions, to 1.64 eV at 11.5 GPa, with a narrow PL emission composed by two components, with the second one appearing in concomitance with the phase separation and significantly shifted to lower energy. On the other hand, DA2GeI4, changes from a non-PL system at ambient pressure, to a clear broadband emitter centered around 730 nm (FWHM ~ 170 nm), with a large stoke shift, and an intensity maximum at about 3.7 GPa. This work sheds light on the structural stability of 2D perovskites characterized by extended alkyl chains, to date limited to four carbon atoms, and shows the pressure-induced emergence of broad emission in a novel lead-free perovskite, DA2GeI4. The evidence of wide emission by a moderate pressure in a germanium-based 2D MHP represents a novel result which may open the design, by chemical pressure, of efficient wide or even white lead-free emitters.

Metal Complexes of π-Expanded Ligands (8): Cold Crystallization of bis[2-[(octylimino)methyl]-1-pyrenolato-N,O] copper(II) by Thermal Analyses, Magnetic Studies, and FT-IR

Molecules exhibiting cold crystallization, an exothermic phenomenon in heating following supercooling, can be used as a heat-storing material. On the other hand, examples in non-polymers are still few. To test metal complexes as potential compounds for heat-storage materials, a salicylaldiminato-typed copper(II) complex, bis[2-[(octylimino)methyl]-1-pyrenolato-N,O] copper(II) 1(Cu), which had two different coloured forms and a characteristic long alkyl chain, exhibited complicated thermal behaviour including cold crystallization. The long alkyl chain was a steric barrier to molecular stacking, leading to the supercooled state. Besides, the two polymorphs were characterized by IR spectra studies and magnetic susceptibility.

Synthesis of Alkyl Aliphatic Hydrazine and Application in Crude Oil as Flow Improvers

In this paper, alkyl aliphatic hydrazine, which is different from traditional polymer fluidity improver, was synthesized from aliphatic hydrazine and cetane bromide, and evaluated as a pour point and viscosity-reducer depressant for crude oil. The evaluation results showed that alkyl aliphatic hydrazone fully reduced the pour point and viscosity of crude oil with the increase of crude oil fluidity. The viscosity reduction rate of crude oil in Jinghe oilfield was 79.6%, and the pour point was reduced by about 11.3 °C. The viscosity reduction rate of crude oil in Xinjiang Oilfield was 74.7%, and the pour point was reduced by 8.0 °C. The long alkyl chain is beneficial to the eutectic of wax in crude oil, and the polar group inhibits the crystal growth, resulting in the decrease of pour point and viscosity. The waste oil is fully recycled into oilfield chemicals.